Basic technology of 3D printers of so-called fused-deposition-modeling type, which use ABS resin or PLA resin filament, is described in the U.S. Pat. No. 5,136,515 by Richard Helinski. In addition, there are other types of 3D printers that use material that is in gel-state in room temperature but becomes solid by heat or light. By using such technologies, object models to be printed are sliced to thin layers, and each layer is formed by arraying filament horizontally, and the layers are stacked.
Upper-layer filaments must be supported either by the print bed, by lower-layer filaments, or by support material, so they do not usually be placed (printed) appropriately without support. However, under certain conditions, they can be supported by filaments in oblique direction so they can overhang, but the overhang angle is restricted; that is, the angle must be smaller than 60 (or 75) degrees so it is not possible to array filaments horizontally (i.e., 90 degrees angle).